Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 54 Ecosystems

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems while matter cycles within them

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Conservation of Energy Laws of physics and chemistry apply to ecosystems, particularly energy flow The first law of thermodynamics states that energy cannot be created or destroyed, only transformed Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter Prokaryotes and fungi are important detritivores Decomposition connects all trophic levels

Fig Microorganisms and other detritivores Tertiary consumers Secondary consumers Primary consumers Primary producers Detritus Heat Sun Chemical cycling Key Energy flow

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gross and Net Primary Production Total primary production is known as the ecosystem’s gross primary production (GPP) Net primary production (NPP) is GPP minus energy used by primary producers for respiration Only NPP is available to consumers Ecosystems vary greatly in NPP and contribution to the total NPP on Earth Standing crop is the total biomass of photosynthetic autotrophs at a given time

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area Marine ecosystems are relatively unproductive per unit area, but contribute much to global net primary production because of their volume

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Nutrient Limitation More than light, nutrients limit primary production in geographic regions of the ocean and in lakes A limiting nutrient is the element that must be added for production to increase in an area Nitrogen and phosphorous are typically the nutrients that most often limit marine production Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth off the shore of Long Island, New York

Fig Primary producers 100 J 1,000,000 J of sunlight 10 J 1,000 J 10,000 J Primary consumers Secondary consumers Tertiary consumers

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The green world hypothesis proposes several factors that keep herbivores in check: – Plant defenses – Limited availability of essential nutrients – Abiotic factors – Intraspecific competition – Interspecific interactions

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 55.4: Biological and geochemical processes cycle nutrients between organic and inorganic parts of an ecosystem Life depends on recycling chemical elements Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

Fig a Precipitation over land Transport over land Solar energy Net movement of water vapor by wind Evaporation from ocean Percolation through soil Evapotranspiration from land Runoff and groundwater Precipitation over ocean

Fig b Higher-level consumers Primary consumers Detritus Burning of fossil fuels and wood Phyto- plankton Cellular respiration Photo- synthesis Photosynthesis Carbon compounds in water Decomposition CO 2 in atmosphere

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Terrestrial Nitrogen Cycle Nitrogen is a component of amino acids, proteins, and nucleic acids The main reservoir of nitrogen is the atmosphere (N 2 ), though this nitrogen must be converted to NH 4 + or NO 3 – for uptake by plants, via nitrogen fixation by bacteria Organic nitrogen is decomposed to NH 4 + by ammonification, and NH 4 + is decomposed to NO 3 – by nitrification Denitrification converts NO 3 – back to N 2

Fig c Decomposers N 2 in atmosphere Nitrification Nitrifying bacteria Nitrifying bacteria Denitrifying bacteria Assimilation NH 3 NH 4 NO 2 NO 3 + – – Ammonification Nitrogen-fixing soil bacteria Nitrogen-fixing bacteria

Fig d Leaching Consumption Precipitation Plant uptake of PO 4 3– Soil Sedimentation Uptake Plankton Decomposition Dissolved PO 4 3– Runoff Geologic uplift Weathering of rocks

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Agriculture and Nitrogen Cycling The quality of soil varies with the amount of organic material it contains Agriculture removes from ecosystems nutrients that would ordinarily be cycled back into the soil Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly affects the nitrogen cycle Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

Fig

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Acid Precipitation Combustion of fossil fuels is the main cause of acid precipitation North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid – pH 5.6 or less Acid precipitation changes soil pH and causes leaching of calcium and other nutrients

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Toxins in the Environment Humans release many toxic chemicals, including synthetics previously unknown to nature In some cases, harmful substances persist for long periods in an ecosystem One reason toxins are harmful is that they become more concentrated in successive trophic levels Biological magnification concentrates toxins at higher trophic levels, where biomass is lower PCBs and many pesticides such as DDT are subject to biological magnification in ecosystems In the 1960s Rachel Carson brought attention to the biomagnification of DDT in birds in her book Silent Spring

Fig Lake trout 4.83 ppm Concentration of PCBs Herring gull eggs 124 ppm Smelt 1.04 ppm Phytoplankton ppm Zooplankton ppm

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Rising Atmospheric CO 2 Levels Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO 2 has been steadily increasing

Fig CO 2 CO 2 concentration (ppm) Temperature Average global temperature (ºC) Year

Fig

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Greenhouse Effect and Climate CO 2, water vapor, and other greenhouse gases reflect infrared radiation back toward Earth; this is the greenhouse effect This effect is important for keeping Earth’s surface at a habitable temperature Increased levels of atmospheric CO 2 are magnifying the greenhouse effect, which could cause global warming and climatic change

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Depletion of Atmospheric Ozone Life on Earth is protected from damaging effects of UV radiation by a protective layer of ozone molecules in the atmosphere Satellite studies suggest that the ozone layer has been gradually thinning since 1975 Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such as CFCs produced by human activity

Fig O2O2 Sunlight Cl 2 O 2 Chlorine Chlorine atom O3O3 O2O2 ClO

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased